Mountain Mint is a native erect perennial forb, growing up to 3 feet high on 4-angled stout stems that have short white hair along the ridge lines. Stems branch frequently and will have a reddish tinge on older plants.
The leaves are small, opposite, lance shaped and rounded at the base with pointed tips, smooth margins and usually without stalks. The largest leaves will be 2-1/2 inches long and only 1/5th as wide. Foliage is sweetly aromatic when crushed.
The inflorescence consists of dense umbel-like clusters of small flowers at the tips of stems. Each umbel has 4 or more flowers, some as many as 50. The inflorescence will be about 3 inches wide on mature plants. Under the cluster are small green pointed leaf-like bracts.
The flowers are 5-parted, about 1/8 inch long with a calyx that has 5 triangular teeth, and a white tubular corolla forming two spreading lips, with, typical of many mint family flowers, the upper lip of the flower divided into two lobes or just notched. The lower lip is singular or subdivided into 3 lobes. There is white hair on the outside of the corolla and conspicuous purple spots on the inside. The 4 stamens have white filaments and yellow to purplish anthers. The single style is white and exserted. Flowers open at different times, beginning at the outer edges of the cluster.
Seed: Fertile flowers mature to a brown dry capsule that contains 4 minute brownish-black seeds which are distributed by wind when the stem is shaken. Seeds are ovoid-cylindrical, angled, with one blunt rounded end and one more pointed rounded end. The seed capsules are long brown tubes tightly clustered together in the flower head. Seeds need light for germination and warm soil, but do not need cold stratification. They should be surface sown.
Habitat: The root structure consists of small rhizomes with a mass of fibrous roots. It spreads readily and can be invasive. It grows in most soil types, prefers full sun is adaptive to wet to dry-mesic moisture conditions.
Names: The genus name Pycnanthemum, is derived from two Greek words - pyknos meaning 'dense' and anthos, meaning 'a flower' - together referring to the densely flowered clusters. The species virginianum, would be "of Virginia" where first described. The plant classification authorship is quite complex - see notes below.
Above and Below: The inflorescence has dense umbel-like clusters of small flowers at the tips of stems. The flowers are 5-parted, about 1/8 inch long with a calyx that has 5 triangular teeth, and a white tubular corolla forming two spreading lips, white hair on the outside and with with conspicuous purple spots on the inside.
Below: 1st photo - The stalkless lance shaped leaves with rounded base. 2nd photo - The typical square stem of the mint with fine short hair.
Right: The root structure consists of small rhizomes with a mass of fibrous roots.
Below: 1st photo - clusters of the seed capsules from the drying flower head. 2nd photo - The minute (less than 1 mm) brownish-black seeds.
Below: There is a nice grouping of these plants in the Garden near the intersection of Prairie Path and Blazing Star Boulevard. These blooms in early to mid-July.
Notes: Virginia Mountain Mint is considered indigenous to the Garden. Eloise Butler noted the presence of the plant in her log on July 28, 1918. She planted it in 1922. Martha Crone first reported planting this species on Sept. 28, 1937 and again in 1946. The plant was listed on her 1951 inventory of plants in the Garden at that time. Cary George noted planting it in 1995. It is native to Minnesota and is found in most counties with most exceptions the very north and far NE. In North America it is found from the central plains eastward except for the southern coastal region. In Canada, east of Manitoba. There is little reference to this plant in the lore books. This is the only other member of this genus found in Minnesota on the current DNR survey list (2019). At one time P. flexuosum, Appalachian Mountain Mint was reported but it has never been collected. However, it is interesting that on July 28, 1918 Eloise Butler commented in her Garden Log that P. virginianum was the more fragrant species of the two and that P. flexuosum was indigenous in the northwest gentian meadow of the Garden.
Scientific name authorship: The original description of this plant was given by 'L.' which refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. Then two others revised his work - - ‘T.Dur.’ is for Theophile Alexis Durand (1855-1912) French/Belgian botanist and ‘B.D.Jacks.’ is for Benjamin Daydon Jackson (1846-1927) English Botanist and author of Index Kewensis. The next two authors amended the work of those first two but give them credit by leaving their names in the chain - those final two (the 'ex') are ‘B.L.Rob.’ is for Benjamin Lincoln Robinson, (1864-1935) American Botanist and ‘Fernald’ is for Merritt Lyndon Fernald (1873-1950) American botanist, Harvard Professor, scholar of taxonomy, author of over 850 papers, editor of the 7th & 8th editions of Gray’s Manual of Botany.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"